Efforts have been made to curtail a risk of cooking fires from an electric stove.
U.S. Pat. No. 6,246,033 provides a method and apparatus for controlling operation of a range-top coil heating element. After ten years of use in the market, this device still has not received wide-spread acceptance. Specifically, when installed on test ranges the applicant, the device has consistently prevented water from boiling.
The applicant developed the technology of U.S. Pat. No. 9,220,130, which is a substantial improvement over prior art constructions for range-top coils. However, neither of these patents address abnormal operation of cooking elements within an electric oven which are commonly referred to as the bake and broil elements.
UL858 is a standard for Safety of Household Electric Ranges. Section 72 prescribes a series of tests for abnormal operation. To pass some of these tests, no molten or flaming material can be ejected from the unit, no compromised electrical wiring, no scorching of cheesecloth within the test enclosure, and a fuse in line with the grounding conductor cannot open.
There are two known prior art techniques which can assist in passing the safety standard. First, one can limit the overall wattage generated by heating elements within the oven. However, while this can provide a safe oven, it requires a balance to find a wattage whose heat input can match an equilibrium of heat loss to maintain oven temperatures that should not place the wiring or other electrical components in jeopardy. The wattage limitations can permit the cooking appliance to pass the standards without a need for additional safeguards. However, this technique can also limit the oven's utility such as requiring longer than desired time to preheat to cooking temperatures.
The second technique known to be used to pass the safety standard is to provide redundant controls within the oven walls (not within the cooking chamber of the oven). The redundant controls act as a safety switch to secure electrical flow to at least one of the terminal connections (normally a female spade connection) which connect to one of the bake and broil elements to thereby prevent the flow of electricity through the affected bake/broil element when reaching a predetermined condition. A mechanical safety switch circuit has been used by at least some manufacturers which provides for the sensing of temperature, and if exceeding a predetermined amount, disengaging a connection to thereby prevent flow of electricity to the bake/broil element(s) at a location between the terminal connecting to the element and the temperature controls. By interrupting the circuit, damage to the cooking appliance and possibly the home can be prevented. Once temperature near the sensor drops, the switch can reset the circuit.
This second method requires additional controls which will likely need to be subjected to separate independent testing. Technical expertise or engineering will likely dictate the location of the circuitry and sensing location so as to produce safe and repeatable results. Furthermore, if the temperature for the circuit is set too low, the circuit could prevent normal cooking operations even when there is no overheating condition present. If the setting is too high, the circuitry might fail to perform its safety function as intended.
Accordingly, an improved electric oven and/or bake elements and/or broil elements is believed to be desirable in the marketplace.